Obesity is now recognized as a serious chronic disease, but there is pessimism about how successful treatment can be. A general perception is that almost no one succeeds in long-term maintenance of weight loss. To define long-term weight loss success, we need an accepted definition. We propose defining successful long-term weight loss maintenance as intentionally losing at least 10% of initial body weight and keeping it off for at least 1 year. According to this definition, the picture is much more optimistic, with perhaps greater than 20% of overweight/obese persons able to achieve success. We found that in the National Weight Control Registry, successful long-term weight loss maintainers (average weight loss of 30 kg for an average of 5.5 years) share common behavioral strategies, including eating a diet low in fat, frequent self-monitoring of body weight and food intake, and high levels of regular physical activity. Weight loss maintenance may get easier over time. Once these successful maintainers have maintained a weight loss for 2-5 years, the chances of longer-term success greatly increase.